Spring with different stiffness in compression and tension

As you may know, we can define a spring element between two points by using the Special menu in the Interaction module to define Springs/Dashpots features:

(Here, to have a very simple model, we have defined two Reference Point in Assembly module before.)

In Edit Springs/Dashpots window that appeared after selecting two points, you can define spring stiffness:

This stiffness will be same for tension and compression. If you want to define different tensile and compressing stiffness, you must bother yourself more using Abaqus Keywords editor:

Now, you can see the keywords created by Abaqus automatically due to graphical commands in Abaqus/CAE when creating the spring:

By adding the nonlinear term in the spring definition block (*Spring keyword) one could then define Spring behavior which is different for compression and tension. Just click on the *Spring… line and edit the block as below:

(When you start editing, the color of affected block will turn into pink)

The data line added are:

Force1, Displacement-1

0.0, 0.0

Force3, Displacement-3

This new block means that when you apply -1.0 m displacement, the spring will create 200 N force, so K=F/x=200/1=200 N/m. This is the stiffness in compression. Then you define tensile stiffness by saying 1.0 m displacement for 100 N force. This is K=100 N/m (as before).